I have ridden both the trails mentioned above and agree that the crushed limestone surface, while "environmentally friendly", does have it's drawbacks. It's rolling resistance is noticably higher than any blacktop surface, particularly when wet, and it is really dusty in the dry.I have ridden an number of crushed limestone trails. It is cheaper than blacktop, but the rolling resistance is higher and I don't know how that affects you ADA requirements. Runoff does not seem to be an issue.Not only is the rolling resistance higher, but it can be dusty when dry, which is not friendly to drive trains. And it is susceptible to washouts - a preventable issue with adequate engineering of ditches and culverts. On the good side, any of these softer trail materials are more forgiving too tree roots that pass beneath them than asphalt which produces tell-tale cracks and bumps.
It can be ridden on road tires and I have used a street bike with 700x23 tires but wider Hybrid or semi-slick MTB tires work a lot better. As to wheelchairs, I think it would be very difficult for them and I wouldn't want to have to push one more than a very short distance on such a surface.